Beyond the 6-Speed: More Ratios for Automatic Transmissions

GENERAL MOTORS and Ford next month are expected to announce an agreement that will pave the way for the automakers to jointly develop new automatic transmissions designed for improved fuel economy.

The deal will enable G.M. and Ford engineers to study and possibly share a variety of future transmission designs, with an eye toward a manufacturing alliance, according to sources at both companies who declined to be identified because they were not authorized to speak about future product plans. The automakers are known to have 8-, 9-, and 10-speed automatic transmissions in development for front- and rear-wheel-drive cars and light trucks.

With the agreement, the companies, longtime Detroit rivals in most matters, are once again cooperating in a venture that could save them billions on technologies critical to meeting stringent new federal fuel economy regulations set for 2017 as well as similar standards coming in Europe.

If the relationship evolves into a joint production program, “it would have huge manufacturing cost and volume advantages over all the competition,” because of the combined size of G.M. and Ford and their supply base, said Skip Nydam, who tracks transmission developments for ND-Automotive, an industry analyst firm.

G.M. and Ford already are successful in working together on transmissions. In 2002, they agreed to share design and production of a new 6-speed automatic for front-drive vehicles. The resulting Ford 6F and G.M. 6T70 transmissions, introduced in 2006 and numbering over 8 million produced, use common mechanical parts but have electronic controls specific to their applications. The independently developed electronics tailor the transmissions to nearly 30 different models.

The auto industry’s race toward a greater number of transmission gears now resembles that of the bicycle industry of 25 years ago, when 10-speed bikes were left in the dust by those with 12, 15 and more speeds. But there’s no comparison in the investment required. Experts say there is not much change left from a billion-dollar investment in a new automatic gearbox that will be produced in numbers of at least 500,000 a year.

Automakers that buy new transmission designs from specialist suppliers like ZF in Germany and Aisin in Japan, rather than designing and manufacturing their own, typically pay royalties on intellectual-property rights and license fees for each transmission, adding to the vehicle’s cost.

“The biggest benefit in G.M. and Ford working together is it reduces their investment risk,” said David Petrovski, a powertrain analyst at IHS Automotive.

“It’s just not economically feasible for them to separately chase after every new fuel-efficiency technology under the sun,” he said. “By collaborating, they’re able to use the best engineering concepts from both sides.”

Automatic transmissions with more gear ratios and more sophisticated electronic controls are crucial to improving fuel economy. Mr. Petrovski noted that as automakers replace existing engines with smaller turbocharged versions that use less fuel, the engines typically have to operate at higher speeds to produce maximum output. He cited the industry’s steady march from 3- and 4-speed automatics in the 1980s to 5- and 6-speeds in the 1990s, then the jump to 7- and 8-speed transmissions in the early 2000s. Chrysler is preparing to release a 9-speed automatic, designed by ZF, in 2013.

Adding more gears helps to keep the engine operating in a speed range where it has the best performance with the least fuel consumption. An 8-speed automatic can deliver up to 11 percent better fuel economy than a 6-speed, for example, depending on engine, vehicle and drive-axle gearing.

An important factor in the move to seven and more gears is the transmission’s ratio spread — the numerical relationship between first and top gear (called the overall ratio spread), or between adjacent gears — for instance, third and fourth gears.

Adding more gears is the only way to have a large overall ratio spread (for both good acceleration and quiet highway cruising) along with a small ratio spread between gears (to keep the engine revving at its best power level for a given road speed). The higher the number, the better. The new 9-speeds will have a ratio spread close to 10, compared with a typical 6-speed’s ratio spread of about six.

Packing more gears into the compact transmission housings used in smaller vehicles — along with the hardware needed to deliver smooth, imperceptible shifts — is an increasingly tricky challenge, engineers say. They are designing the gearsets to “nest” within each other to save space.

However, there is only so much space available under the hood of subcompact and compact cars with front-wheel drive, in part because their transmissions are positioned across the chassis, rather than lengthwise as in trucks, large S.U.V.’s and most sports cars and large luxury sedans. The limited width between the front wheels restricts how wide the transmissions can be — and the number of gears that can fit inside.

The lack of space to package seven and more gears is one reason that subcompacts like the Ford Fiesta and Chevrolet Sonic don’t achieve higher fuel efficiency than the larger Ford Focus and Chevy Cruze. It’s also why compacts like the Focus and Cruze can’t top the economy of the midsize Fusion and Malibu. (The longer vehicles also have lower aerodynamic drag, which helps overall efficiency.)

The tiny Chevrolet Spark had only enough space in its engine compartment to accommodate a 4-speed automatic. To quickly satisfy demand for more gear ratios from American customers who don’t want the standard 5-speed manual, G.M. plans to offer a continuously-variable transmission, supplied by Jatco, a Japanese C.V.T. specialist, in coming Sparks. The compact C.V.T. essentially offers an infinite number of gear ratios, enabling the tiny car to close the fuel-economy gap with its larger, more expensive stablemates.

Correction: October 7, 2012

A timeline last Sunday with an article about innovations in automatic transmissions misidentified the first car with a continuously variable gearbox. It was the 1959 DAF 600, not the Volvo 343. A caption with the timeline also misstated the model year of the Chrysler Town & Country depicted. It was a 1949 model, not a 1940.

A version of this article appears in print on September 30, 2012, on page AU2 of the New York edition with the headline: Beyond the 6-Speed: More Ratios for Automatic Transmissions. Order Reprints|Today's Paper|Subscribe